Abstract
Observations of high-contrast scenes through an atmosphere are subject to the adjacency effect—the artificial brightening from photons that have scattered in the atmosphere such that they appear to originate from the dark rather rather than the bright surface. In this work, we examine how the adjacency effect manifests in imaging of the surface of Titan, Saturn’s largest moon, through the example case of a particularly high spatial resolution observation of a 100 km lake at Titan’s north pole, Kivu Lacus. We find that the adjacency effect can increase the brightness of dark surfaces up to 10% at 5 μm, while observations at 2 μm may be brightened up to 1%. Shorter wavelengths are so dominated by multiple scattering that all directionality is lost; atmospheric scattering swamps any observable adjacency effect. The bidirectional reflectance distribution function modifies both the directionality and magnitude of the adjacency effect, maximizing the effect in the downsun direction for specular surfaces. High-resolution observations (∼1 km) of high-contrast scenes on Titan will need to take into account the adjacency effect at 2 μm, but the effects at longer wavelengths (or at lower atmospheric opacity) may be smaller than the pixel scale such that observed reflectance heterogeneities are more likely due to actual properties of the surface.